1. Field of the Invention
This invention relates to thermoplastic, pressure-sensitive solid adhesives capable of transferring an adhesive film to a substrate by friction rubbing of the adhesive on the substrate. The adhesives of this invention consist essentially of polyisobutylene (PIB), wax, and optionally an adhesion promoter resin, all within certain proportions, molecular weights, melting points, or hardness.
2. Background Art
Crayon adhesives are well known. Many such adhesives use solvents which normally dry out and require lipstick type containers. Illustrative of such solvent containing crayon adhesives there can be mentioned U.S. Pat. No. 3,929,694 to Peter S. Columbus which issued on Dec. 30, 1975.
U.S. Pat. No. 2,142,039 to A. Abrams et al. of Dec. 27, 1938 discloses a pressure-sensitive composition and sheets coated with such composition. The composition is applied to the sheets by melting the composition and coating the sheets wherein the composition comprises: 15% to 60% of a cohesive agent such as isobutylene polymer, ethyl cellulose or various rubbers; 10% to 50% of an adhesive agent such as rosin; 5% to 45% of a plasticizer such as mineral oil, triphenyl phosphate, etc. and 4% to 45% of a wax modifier such as a microcrystalline wax.
U.S. Pat. No. 2,560,916 to P. Barnhart, et al. of Jul. 7, 1951 relates to a laminating cement composition for plies of paper which comprises: 1 to 25 parts of PIB; 1-30 parts of resin; 95 to 50 parts of microcrystalline wax; and 0 to 20 parts of a plasticizer. It appears that the plies of paper are heat sealed by the cement.
U.S. Pat. No. 3,267,052 to G. Brennan of Aug. 16, 1966 discloses a pressure-sensitive, thermoplastic adhesive which is shaped into a crayon-like body. The adhesive crayon transfers adhesive to paper by rubbing the crayon on paper. The adhesive remains pressure-sensitive for a short period of time during which a second sheet of paper can be adhered to the first by contact with the rubbed-on adhesive. The adhesive comprises: a hard resin, such as those referred to herein as tackifiers and adhesion promoter resins; soft rubber such as plasticized natural rubber, plasticized butyl rubber and PIB having a molecular weight of 1,000 to 25,000; and a soft wax such as Japan wax, ozokerite, paraffin, stearic acid and certain microcrystalline waxes. Additionally, the use of plasticizing oils are described as desirable. This patent also discusses a prior adhesive which contained a low molecular weight polymer of isobutylene and a tacky blend of microcrystalline waxes which produced a weak and temporary bond.
The main differences of the above discussed Brennan patent from the instant invention are: a) Brennan requires soft waxes in his adhesives whereas in the instant invention relatively hard waxes are used. Brennan also uses plasticizing oils and butyl latex to soften the adhesives. b) The PIB and other soft rubbers of Brennan are described as non-solids of low molecular weight such as from 1,000 to 25,000 and the specific examples as to PIB are at a molecular weight of 10,000. Brennan does not give the method used for determining his molecular weight. The PIB used in the instant invention is a semi-solid and is believed to be of generally higher molecular weight. c) Brennan requires the use of a hard resin for obtaining a permanent bond whereas the instant invention does not require a hard resin and indeed, use of the amount of resin preferred by Brennan, namely, about 52% in applicants' composition provides an unsatisfactory product. d) Brennan requires at least three ingredients in order to obtain a permanent bond in his formulations, whereas only two ingredients are required in the instant invention for a permanent bond. Thus, Brennan describes his adhesives which do not contain the hard resin as mild and temporary adhesives. e) Brennan states that he requires soft waxes to maintain pressure-sensitive properties for a period of time to prevent the applied adhesive film from becoming hard and tackles within a few seconds after application whereas the pressure-sensitive properties of the applied adhesive film of the instant invention are long lasting such as at least half an hour or more. f) The quantity of PIB used in Brennan is from about 1% to 35% whereas the amount used in the instant invention is at least 40%. g) The hard resin (adhesion promoter resin) in Brennan varies from about 15% to 75% of the composition with the preferred amount being about 52% whereas in applicant's invention, the operability of the adhesive promoter resin is within a relatively narrow range at a relative low concentration and when used in quantities of about 52% the crayon adhesive of this invention was inoperable and above 30% the crayon adhesive of this invention has poor properties. h) Hard waxes are optional in Brennan in addition to the soft waxes. Penetration values of such waxes are not given, but many of the waxes listed by Brennan as optional hard waxes are applicant's preferred waxes. i) Brennan uses many waxes of low melting point which have poor stability on storage and shipping during hot weather.
U.S. Pat. No. 3,423,342 to E. Kendall of Jan. 21, 1969 discloses a solid adhesive mass, which is essentially free of surface tack but capable of transfer of an adhesive film to a substrate by friction rubbing of the mass on the substrate. The composition consists essentially of a homogeneous blend of 53-75 parts of a tack promoting rosin derivative, about 10 to 33 parts of a copolymer of ethylene and vinyl acetate, from a small but effective amount for making the mass substantially free of surface tack up to about 5 parts of paraffin wax and a small but effective amount for friction disposition of the film up to about 25% of a plasticizer such as a sebacic acid alkyd.
U.S. Pat. No. 3,471,419 to J. Ehrlich of Oct. 7, 1969 discloses a filled foam product which can be cut in strips and used as a toy. The filling comprises a microcrystalline wax having a needle penetration value of about 15 to 80 compounded with at least one of polyethylene or PIB, a plasticizer for the microcrystalline wax and plasticized polystyrene resin.
U.S. Pat. No. 4,468,254 to N. Yokoyama et al of Aug. 28, 1984 discloses a wax emulsion for waterproofing various materials. The emulsion comprises: water; a hydrocarbon wax; and a liquid polybutadiene, a polybutene or a PIB.
U.K. Pat. No. 692,945 to Industrial Tape Corporation which was published on Oct. 8, 1949 discloses adhesive tapes which are applied by heat and pressure. The tapes are coated with adhesive on one side and a wax or wax together with a wax compatible polymer such as polyethylene or PIB on the other side. However, amoung other shortcommings of this U.K. patent, the quantity of PIB is not greater than 25% of the adhesive.